Welcome to a webinar that will focus on a fundamental aspect of wetting phenomena, namely contact angle hysteresis and static and dynamic drop friction!
When: Tuesday 23 January, 2024. 13:00–15:00 CET
Where: Online-only via Zoom
Title: Fundamental aspects of wetting – drop friction
Speakers: Prof Hans-Jürgen Butt, Max Planck Institute for Polymer Research, Germany, and Prof Joël de Coninck, University of Mons, Belgium
Description
This second ECIS webinar will focus on a fundamental aspect of wetting phenomena, namely contact angle hysteresis and static and dynamic drop friction.
Speaker 1 will posit that electric charges, spontaneously left on the surface by sliding water drops, can substantially influence contact angles through electrostatic interactions and thus hinder roll-off. The effect occurs for a wide range of surfaces and aqueous electrolytes, and can be quantitatively explained by two mechanisms: Electrocapillarity, and an increase in effective surface energy of the solid surface behind the drop. Starting from the point that both static and dynamic friction are important in understanding the behavior of moving objects.
Speaker 2 will ask the questions: Can we combine the knowledge we have for solid/solid friction to what is known for a liquid/solid system, or vice-versa, to improve our capability to predict what friction will be from basic measurements and mechanisms? It will be shown that dynamics of spreading or wetting is very often controlled by dynamic friction.
Questions posed by registered members of the audience will be addressed, please send questions in advance to:
Leontidis Epameinondas email: leontidis.epameinondas@ucy.ac.cy or
Pierandrea Lonostro email: pierandrea.lonostro@unifi.it
Agenda
Section I: H.-J. Butt (45 mins + 15 mins questions from the audience)
Abstract:
Whether a liquid drop sticks to a surface or rolls off it depends on contact angle hysteresis—the difference between the angles formed at the advancing and receding contact lines of a moving drop. While having been researched for a century, established theories have overlooked one essential contribution to contact angle hysteresis. We show that electric charges, spontaneously left on the surface by sliding water drops, can substantially influence contact angles through electrostatic interactions and thus hinder roll-off. The effect occurs for a wide range of surfaces and aqueous electrolytes. We explain the effect quantitatively by two mechanisms: Electrocapillarity and an increase in effective surface energy of the solid surface behind the drop.
X. Li, A.D. Ratschow, S. Hardt, H.-J. Butt, Phys. Rev. Lett., accepted.
Section II: J. de Coninck (45 mins + 15 mins questions from the audience)
Abstract:
Friction is a force that opposes motion between two surfaces that are in contact. It is caused by the interactions between the molecules at the two surfaces. There are various models for friction, but they all involve parameters which must be measured or fitted, hence the detailed mechanisms involved in friction are still a matter of discussion.
Static friction is the force that resists the motion of an object when it is at rest and is pushed or pulled. Kinematic or dynamic friction is the force that opposes the motion of an object that is already in motion. Both types of friction are important in understanding the behavior of moving objects. Can we combine the knowledge we have for solid/solid friction to what is known for a liquid/solid system, or vice-versa, to improve our capability to predict what friction will be from basic measurements and mechanisms? The aim of the presentation is precisely to review this issue [1].
Using large scale numerical simulations, experiments, and theoretical considerations, we will focus on sliding drops to study the case of static friction. We will also show how this mechanism can be used to design smart surfaces.
Complementary to the static aspect, we will show that dynamics of spreading or wetting is very often controlled by dynamic friction. Here again, we will use different techniques to illustrate the mechanism such as numerical simulations, experiments, and theories.
By building new bridges between areas of science that had been seen as different until now, we can only continue to marvel more and more at the beauty of Nature.
[1] J. De Coninck (2022) “An Introduction to Wettability and Wetting Phenomena”. In: Marengo M., De Coninck J. (eds) The Surface Wettability Effect on Phase Change. Springer, Cham. https://doi.org/10.1007/978-3-030-82992-6_2
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Hans-Jürgen Butt studied physics in Hamburg and Göttingen. He did his PhD at the Max Planck Institute for Biophysics with Ernst Bamberg, Frankfurt, in 1989. After a postdoc in Santa Barbara with Paul Hansma and a researcher position back in Frankfurt in the group of Ernst Bamberg, he became associate professor at the University Mainz and three years later full professor at the University of Siegen. In 2002 he joined the Max Planck Institute for Polymer Research in Mainz as a director. His research is on the structure and dynamics of soft matter interfaces in particular wetting and surfaces forces using methods such as scanning probe microscopy, fluorescence correlation spectroscopy and X-ray scattering.
Joël de Coninck received a MSc in Physics (1978) and another in Mathematics (1980) and he obtained his PhD degree (1983) from the University of Mons in the Theoretical Physics group,
working on a new probabilistic approach of the renormalization group to describe critical phenomena. He then made long-stay visits to centers such as Oxford, Caltech (Pasadena), Ecole Polytechnique (Paris). He got a permanent position at the University of Mons in 1985, where he has been a full Professor until 2021. He has also been a visiting Professor in several overseas universities. His main area of expertise is focused on wetting, spreading, and coating, combining experimental and computational/theoretical methods.
Contact:
For practical questions, please send an email to josefin.martell@linxs.lu.se
The webinar is organised by the Europan Colloid and Interface Society, in partnership with LINXS.
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